1. Field of the Invention
This invention relates to a method of achieving an improved carbonaceous fuel composition. More particularly, this invention relates to an improved method of removing gangue materials from coal to form a low-sulfur, low-ash carbon fuel that burns readily with high efficiency and low pollution emissions.
2. Description of the Prior Art
The prior art has seen development of many and varied processes for treating coal for different purposes. Typical of these processes are those described in issued U.S. patents such as the following: U.S. Pat. Nos. 2,133,280 describing preparation of mineral oil products by extraction of coal; 3,748,254 describing the conversion of coal by solvent extraction; 3,754,876 describing the upgrading of coal by heating lumps to pyrolysis temperatures of up to 1000.degree. F. (Farenheit) in an inert hydrogen-poor hydrocarbonaceous heat transfer fluid; 3,856,658 directed to slurried solids in hydrogenation of coal and 3,920,418 directed to converting the coal to a liquid and gaseous fuel employing solvent extraction followed by carbonization of the solids-rich fraction to char, that is finally gasified.
Despite the large number of processes for producing cleaner burning coal and producing cleaner more reactive feed stocks for coal conversion processes, there still exists a great need for such processes. From a pragmatic point of view, there is a particularly urgent need for processes to accomplish the foregoing economically and with higher efficiencies from the energy consumption standpoint.
The closest prior art of which I am aware is my priorly issued U.S. Pat. No. 4,030,893, entitled "Method of Preparing Low-Sulfur, Low-Ash Fuel," issued June 21, 1977; and the descriptive matter of that patent is embodied herein by reference for details omitted herefrom. That patent described and claimed an economical means for removing relatively large grains of diluent gangue materials (ash-forming and inorganic-sulfur-bearing mineral grains) from coals after comminution by conventional means and screening to minus 8 mesh size, with the majority of the material being minus 100 mesh size. In that patented process, the coal was comminuted in the presence of alcohols either before or after final sizing and the dilute slurry of the coal and alcohols, with various chemical compounds in the solution and with colloidal particles in suspension, was then subjected to a series of settling velocity separation steps to remove the higher settling velocity particles from the lower settling velocity particles. The gangue materials that were freed were freed as discreet particles and remained sufficiently large in size to exhibit relatively high settling velocities resulting from the size, higher density and particle sphericity (roundness) so as to be effectively separated from the lower settling velocity carbonaceous material. The carbonaceous material tends to break down to smaller sizes than the more durable gangue materials. That patent also described additional process steps such as the flashing to produce highly reactive puffed coal particles and the like. The patented process provided economical and useful means for reducing the ash-forming and inorganic sulfur-bearing mineral content of carbonaceous fuels; but was applicable only to those coals or lignites wherein the diluent, or gangue materials, exist within the coal or lignite as grains, or particles, larger than about 30 to 50 microns in size, with the minimum size removable depending upon the density and particle shape factors.
Consequently, although the prior inventions; particularly, the latter; were useful advances, they were limited in breadth of applicability. Moreover, the latter also required significant amounts of alcohols to be left in the carbonaceous particulate fuel. The rapidly escalating costs for the alcohols made this undesirable economically, even though it did improve the fuel quality and combustion characteristics.
Despite all the prior improvements, further advances are needed to provide for removal of much smaller particles of diluent, or gangue materials; to effect substantially complete recovery of the alcohols used in the process; and to effect removal of some of the organic sulfur-bearing compounds from the fuel end product, particularly where it is a carbon-hydrocarbon (CHC) fuel.